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WATCHDOG(4)		     Kernel Interfaces Manual		     WATCHDOG(4)

NAME
     watchdog -- hardware and software watchdog

SYNOPSIS
     #include <sys/watchdog.h>

DESCRIPTION
     The  watchdog facility is used for controlling hardware and software watch-
     dogs.

     The device /dev/fido supports several optional ioctl(2) calls for	configu-
     ration,  and  responds  to a single operational ioctl(2) call, WDIOCPATPAT.
     It takes a single argument which represents a timeout value specified as  a
     power  of	two  nanoseconds,  or-ed with a flag selecting active or passive
     control of the watchdog.

     WD_ACTIVE indicates that the watchdog will be kept  from  timing  out  from
     userland,	for  instance  by the watchdogd(8) daemon.  WD_PASSIVE indicates
     that the watchdog will be kept from timing out from the kernel.

     The WDIOCPATPAT ioctl(2) call will return success if just one of the avail-
     able watchdog(9) implementations supports setting the timeout to the speci-
     fied timeout.  This means that at least one watchdog is armed.  By default,
     this will be a hardware watchdog if one is  present,  but	if  no	hardware
     watchdog is able to process the request, a default software watchdog is en-
     abled.   If the call fails, for instance if none of watchdog(9) implementa-
     tions support the timeout length, all watchdogs are disabled  and	must  be
     explicitly re-enabled.

     To  disable  the  watchdogs pass WD_TO_NEVER.  If disarming the watchdog(s)
     failed an error is returned.  The watchdog might still be armed!

     The optional configuration ioctl(2) commands are listed  here,  along  with
     the  type	of  the  parameter  used.  Examples of their use can be found in
     watchdogd(8).

     WDIOC_SETTIMEOUT int	    set/reset the timer

     WDIOC_GETTIMEOUT int	    get total timeout

     WDIOC_GETTIMELEFT int	    get time left

     WDIOC_GETPRETIMEOUT int	    get the pre-timeout

     WDIOC_SETPRETIMEOUT int	    set the pre-timeout

     WDIOC_SETPRETIMEOUTACT int     Set the action  when  a  pre-timeout  occurs
				    (see WD_SOFT_* below).

     WDIOC_SETSOFT int		    Use an internal software watchdog instead of
				    hardware.	There  is also an external soft-
				    ware watchdog, which is used by  default  if
				    no hardware watchdog was attached.

     WDIOC_SETSOFTTIMEOUTACT int    Set the action when a soft timeout occurs.

     The actions that may be specified for the pre-timeout or the internal soft-
     ware  watchdog are listed here.  Multiple actions can be specified by ORing
     values together.

     WD_SOFT_PANIC  panic

     WD_SOFT_DDB    enter debugger

     WD_SOFT_LOG    log(9)

     WD_SOFT_PRINT  printf(9)

RETURN VALUES
     The WDIOCPATPAT ioctl(2) returns zero on success and non-zero on failure.

     [EOPNOTSUPP]	No watchdog present in the kernel or none of the  watch-
			dogs supports the requested timeout value (timeout value
			other than 0).

     [EOPNOTSUPP]	Watchdog could not be disabled (timeout value of 0).

     [EINVAL]		Invalid flag combination passed.

     The  configuration  ioctl(2) operations return zero on success and non-zero
     on failure.

EXAMPLES
	   #include <paths.h>
	   #include <sys/watchdog.h>

	   #define WDPATH  "/dev/" _PATH_WATCHDOG
	   int wdfd = -1;

	   static void
	   wd_init(void)
	   {
		   wdfd = open(WDPATH, O_RDWR);
		   if (wdfd == -1)
			   err(1, WDPATH);
	   }
	   static void
	   wd_reset(u_int timeout)
	   {
		   if (ioctl(wdfd, WDIOCPATPAT, &timeout) == -1)
			   err(1, "WDIOCPATPAT");
	   }

	   /* in main() */
	   wd_init();
	   wd_reset(WD_ACTIVE|WD_TO_8SEC);
	   /* potential freeze point */
	   wd_reset(WD_TO_NEVER);

     Enables a watchdog to recover from a potentially freezing piece of code.

	   options SW_WATCHDOG

     in your kernel config forces a software watchdog in the kernel to	be  con-
     figured  even if a hardware watchdog is configured, dropping to KDB or pan-
     icking when firing, depending on the KDB and KDB_UNATTENDED kernel configu-
     ration options.

SEE ALSO
     watchdogd(8), watchdog(9)

HISTORY
     The watchdog code first appeared in FreeBSD 5.1.

AUTHORS
     The watchdog facility was written by Poul-Henning	Kamp  <phk@FreeBSD.org>.
     The  software watchdog code and this manual page were written by Sean Kelly
     <smkelly@FreeBSD.org>.  Some  contributions  were	made  by  Jeff	Roberson
     <jeff@FreeBSD.org>.

BUGS
     The WD_PASSIVE option has not yet been implemented.

FreeBSD ports 15.1		 January 2, 2018		     WATCHDOG(4)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=watchdog&sektion=4&manpath=FreeBSD+15.1-RELEASE+and+Ports>

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